For shipping and storage, many types of fibrous material can be pressed and bound into bales. Such bales usually have a particular size and shape, depending upon the type and characteristics of the material in the bale and the type of baling machine used. Substantially uniform bales, particularly those having square or rectangular profiles, are advantageous because they usually require no packaging material other than wire, twine, or strapping to hold the bale together and because they can be tightly stacked with minimal space between bales.
A bale of fibrous material may be of relatively low density for any of various reasons. First, the material may contain moisture; a dense bale may not allow material in the interior of the bale to aerate properly, which may cause rotting. Second, an overly dense bale may damage the fibers, especially if they are not oriented properly relative to the compression and binding. Third, dense bales may be too heavy for a person to handle without equipment. Fourth, some materials may be extremely resistant to compaction, resulting in recoil forces on the bindings that exceed the strength of the binding materials. Fifth, material compressed too tightly may become too difficult to separate later when the bale is opened.
However, it is often desirable to bale fibrous material in the densest bale practicable because storage and shipping costs based on volume rather than weight will be lower with denser bales. If the particular material will permit, recompressing low-density bales into high-density bales especially for long-distance shipping may appreciably lower shipping costs, which will make the product more price-competitive in its destination market.
Mown and dried herbaceous forage for livestock is commonly baled for shipping and storage. Hay (alfalfa, timothy, grass, clover, etc.) and straw (stalks of wheat, oats, grass, etc.) are customarily bound in the field into several different types and sizes of bale, in both cylindrical (round bales) and rectangular solid shapes ("rectangular" and "square" bales) having a density of approximately six to ten pounds per cubic foot or less.
Round bales of forage are typically large in diameter (six feet or more) and very low in density. Their size and shape make them difficult to store and transport economically. Consequently, they are usually used only on the farm where the forage was grown, obviating the need for further compression.
Rectangular or square bales of forage are available in a variety of sizes including: 14".times.18" bales in 3- and 4-foot lengths, 16".times.18" bales in 3- and 4-foot lengths, 17".times.23".times.4', 4'.times.4'.times.8', and 3 178 '.times.4'.times.8'. The 14".times.18" and 16".times.18" sizes are the most common. Because rectangular or square bales can be closely stacked, they are the preferred shapes for storing and shipping. However, shipping such bales is usually limited by the space on the transporting vehicle or in the shipping container, which typically can be loaded with more weight than that obtained when the container is fully loaded with low-density field bales.
For example, a typical 40-foot long shipping container has a volume of approximately 2,000 cubic feet and a load limit of 30 tons, or 30 pounds per cubic foot. The minimal current cost is approximately $1,000 to ship a 40-foot container across the Pacific Ocean. If such a container were loaded with hay bales having a density of 10 pounds per cubic foot, the approximate maximum field bale density, the net weight would only be 10 tons, and the shipping cost would be $100 per ton. Costs would be even higher for bales having a density of less than 10 pounds per cubic foot. In other words, because typical field bales are not sufficiently dense to make weight in overseas shipping containers, hay grown domestically and sold overseas is unduly expensive. If bales could be compressed to a mean density of at least 20 pounds per cubic foot, the shipping costs would be reduced to $50 per ton or less.
Increasing the density of bales would also permit more forage to be stored in a given area or volume of space which would tend to decrease storage costs.
There are several problems associated with forming such dense bales, especially of hay or straw. First, dried stems of grasses and other herbaceous forage are mechanically strong and resist compaction. During a typical field baling operation, the stems are usually laid flat and "stacked" inside a rectangular or square bale as a number of transversely oriented layers or "wafers" in a longitudinally extended bale. Because stems of grass or straw are hollow cylinders, which are mechanically very strong structures, a large number of tightly packed stems oriented parallel to the longitudinal axis of the bale would be extremely difficult to compress longitudinally, requiring prohibitively high applied forces. As a result, significant compaction of dried forage is practical only along the longitudinal axis of the bale, where the compaction force is substantially transverse to the axis of the stems. Even so, large magnitude forces are required to achieve bale densities greater than 20 pounds per cubic foot. Extremely large forces are required to achieve densities of 30 pounds per cubic foot or greater.
Second, grass stems are hollow and contain air that can be difficult to expel quickly during compaction. Such trapped air may only slowly be released after extreme compression of the stems, which can cause large post-compaction recoil forces to be exerted on bale bindings at the moment the bale is released from the compaction apparatus, causing the binding material to fail at unacceptably high rates. Such recoil forces are also the result of the mechanical resiliency of forage stems to compaction. Some manufacturers have attempted to solve that problem by using metal wire or metal strapping to bind bales. Unfortunately, however, metal binding material can cause serious injury or death to livestock if ingested.
Third, individual condensed bales should be kept small to limit bale weight so that individual bales can be manually handled without undue difficulty.
Fourth, longitudinal compaction of a hay bale to high density requires an extremely large-magnitude force but only near the end of the compaction stroke. During such a longitudinal compression stroke, the magnitude of force necessary to overcome resistance and achieve a progressively greater bale density increases approximately exponentially relative to a linear increase in density. Likewise, as a bale is longitudinally compressed, the magnitude of force necessary to achieve a progressively shorter bale also increases approximately exponentially relative to a linear decrease in length. If a single hydraulic cylinder were used to perform the entire compaction stroke, the cylinder would have to be sufficiently large in diameter to generate the maximum compression force required at the end of stroke. It would also need to have a long stroke to traverse the long, relatively low-compression portion of the resistance curve. Such large-diameter-long-stroke cylinders, however, require much larger volumes of oil to move the piston a given distance compared to smaller diameter, less powerful cylinders. Pumping such large volumes within acceptable time periods requires large capacity pumps and correspondingly powerful pump-drive motors. Because a compaction apparatus needs to generate high forces only during the last few inches toward maximum stroke, single-cylinder compactors are inherently wasteful of energy; large volumes of oil must be pumped quickly to move a large diameter piston over a long stroke distance over most of which high compression power is not needed. Compaction costs, including energy costs, should be kept as low as possible to ensure that preshipment compression of bales is economically attractive.
Fifth, compression should only be applied along a single axis to minimize the amount of binding material required. If successive compression forces perpendicular to each other were applied to a charge of material, bindings would have to be subsequently applied along each axis of compression in order to maintain the compressed state of the charge. Further, especially with charges such as hay or straw where the fibers are oriented perpendicularly to the axis of the first compression, applying a subsequent compression force parallel to the axis of the fibers may require prohibitively large forces or may damage the fibers.
Several machines have been heretofore used for baling fibrous material, but each has significant drawbacks. Ast (U.S. Pat. Nos. 4,718,335 and 4,676,153) discloses a method and apparatus, respectively, for recompressing bales of fibrous material such as forage. Compression is performed with only one hydraulic cylinder which must be sufficiently large to apply the maximum force required to achieve the desired compaction, thereby necessitating a larger energy expenditure than a multistep compactor using progressively larger and more powerful cylinders of shorter stroke. Also, the Ast apparatus tightly binds fully compressed bales which, even though the bales are "decompressed" by a 30-second maintenance of maximal compression, subjects the binding twine to high recoil forces after the bale is released from the apparatus. Bales compressed more than obtainable with the Ast apparatus would experience an unacceptably high failure rate of bale bindings, despite "decompression," unless metal wire or strapping were used. Further, Ast has no means to ensure uniformity of mass among compressed bales.
Thomas and Logan (U.S. Pat. No. 3,266,096) disclose a multistep compression apparatus wherein the pressure applied in each step to a randomly oriented batch of material is successively increased and applied in a direction perpendicular to that of the previous step. As a result, the material is compressed in all three dimensions. Such an apparatus would not be appropriate for compressing field bales of hay or straw which effectively cannot be compressed to high density in a direction substantially parallel to the axis of the individual stalks.
Stangl (U.S. Pat. No. 3,089,410) discloses an apparatus for pressing light fibrous material, such as cotton or wood pulp, into bales, wherein a bale is built up from successive, volumetrically defined layers of randomly oriented fibers. The Stangl apparatus utilizes only one compression piston which must stroke many times before a full bale is formed. Such an apparatus is simply inappropriate for compressing existing bales of hay or straw to high density in an energy efficient and timely manner.
Several other compaction machines have been patented. However, each is unsuitable for compressing fibrous material along a single axis into high-density bales. For example, Tezuka (U.S. Pat. No. 3,451,190) discloses a device intended to squeeze liquid from trash and garbage, compact it into discrete blocks, and apply a tightly-adhering wrapper therearound. The Tezuka device utilizes four hydraulic cylinders for compaction alone, performed along two axes, as well as additional cylinders for actuation of gates and wrapping equipment. Hence, the Tezuka device would require much larger pumping capacity, and consume more energy and time per bale, than the present invention. More importantly, the Tezuka device applies perpendicular compression forces, which are unsuitable for fibrous material such as hay or straw. Further, the Tezuka device does not show the much simpler concept in the present invention of opposing cylinders that perform sequential compression strokes toward each other and against each other's compression platens. Finally, the Tezuka device is not designed to achieve the degree of compression attainable with the present invention.
Del Jiacco (U.S. Pat. No. 3,996,849) discloses an apparatus for compaction and baling of large, heavy materials such as scrap automobiles. Unlike the present invention, however, only one hydraulic cylinder actually performs the compression. The second cylinder merely elevates the finished bale out of the compression chamber. Hence, the Del Jiacco device is unsuitable for high-density compression of fibrous material for substantially the same reasons as the Ast device, discussed supra.
Fetters (U.S. Pat. No. 4,483,245) discloses a device for compressing and wrapping bundles of large articles, such as cut Christmas trees, in cylindrical "cartridges" for shipment. That device is totally unsuited for compressing charges of hay, straw, or other loose fibrous material into high density bales.
Hence, a primary object of the present invention is to provide a method and apparatus for compressing low-density charges of coarse fibrous material, such as, hay, straw, peat, or other herbaceous forage, into high-density bales having uniform size, shape, and weight for cost-effective shipping over long distances and for economical storage.
Another object of the present invention is to provide a method and apparatus that compresses low-density charges of such fibrous material in an energy-saving and time-efficient manner through a design that eliminates the need to move large, powerful pistons requiring large volumes of oil through long, relatively low-compression strokes and that makes multiple use of hydraulic oil whenever possible, thus saving both power and cycle time.
Another object of the present invention is to provide a method and apparatus that performs the compression from both directions along the longitudinal axis of the charge, allowing control of the dimensional profile of the bale transverse to the axis of compression, minimizing damage to the fibers, and requiring a minimal amount of binding material.
Another object of the present invention is to provide a method and apparatus wherein each charge is overcompressed, plastic strapping applied loosely thereto and the heat-sealed ends of the binding allowed to set, and the charge subsequently allowed to expand into the bindings, thereby alleviating high post-compression mechanical stress on bindings and obviating the need to use metal binding materials.